After doing my BS in engineering physics (with experimental research on gravity), I started my PhD in experimental atomic physics. But I quit to do math, and am now a 4th year student of Michael Hutchings.

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I know light's speed in vacuum is constant, but what about its velocity?@JohnRennie You're not fixing the vacuum, an accelerated observer is the same as a stationary one in a gravitational field. The question refers to the object of light itself, which implicitly assumes you have a fixed observer. If you make an edit which clarifies this, I would gladly remove my downvote.

Destroying currents in superconducting rings by vortex tunnelingThanks for bringing up this related problem; I take it this has negligible effect on the role of SQUIDs. Can you elaborate on your last sentence? I would think the system size $L$ depends on both the ring's thickness $\delta$ and its length $l$. (I initially guessed that the rate of occurrence of vortex tunneling looked like $\text{exp}(-\frac{\delta}{\lambda}\frac{l}{\xi})$, but had no good basis for that guess.)

Magnetic field and electric field induce one another foreverHere is Alred's comment rephrased, in case it helps: The magnetic field and electric field are "one and the same thing", the point being that I can derive the magnetic field from the (changing) electric field and vice versa. So at any point in time for your system (circuit with changing current), the electromagnetic field is $(B(t),E(t))$ and they satisfy the relations that you describe (i.e. the Maxwell equations).

Feb28

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Can you put a magnetic ball into a hollow magnetic sphere?Your statement "If the search for magnetic monopoles ever turns up something, then it will confirm that such a sphere can exist" is false. Monopoles have nothing to do with building a sphere -- the sphere consists of dipoles, and there is no way to create a monopole from a collection of dipoles.